EP2333531A1 - Differentialresonatoren zur NO2-Detektion und damit verbundene Verfahren - Google Patents

Differentialresonatoren zur NO2-Detektion und damit verbundene Verfahren Download PDF

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Publication number
EP2333531A1
EP2333531A1 EP09178792A EP09178792A EP2333531A1 EP 2333531 A1 EP2333531 A1 EP 2333531A1 EP 09178792 A EP09178792 A EP 09178792A EP 09178792 A EP09178792 A EP 09178792A EP 2333531 A1 EP2333531 A1 EP 2333531A1
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EP
European Patent Office
Prior art keywords
functionalized
nitrogen dioxide
sensor
sensing
frequency
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Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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EP09178792A
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English (en)
French (fr)
Inventor
Bogdan-Catalin Serban
Cornel P. Cobianu
Mihai N. Mihaila
Viorel Georgel Dumitru
Octavian Buiu
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Honeywell Romania SRL
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Honeywell Romania SRL
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Priority to EP09178792A priority Critical patent/EP2333531A1/de
Priority to US12/962,067 priority patent/US8563319B2/en
Publication of EP2333531A1 publication Critical patent/EP2333531A1/de
Withdrawn legal-status Critical Current

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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
    • G01N33/0004—Gaseous mixtures, e.g. polluted air
    • G01N33/0009—General constructional details of gas analysers, e.g. portable test equipment
    • G01N33/0027—General constructional details of gas analysers, e.g. portable test equipment concerning the detector
    • G01N33/0036—General constructional details of gas analysers, e.g. portable test equipment concerning the detector specially adapted to detect a particular component
    • G01N33/0037—NOx
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
    • G01N29/02—Analysing fluids
    • G01N29/022—Fluid sensors based on microsensors, e.g. quartz crystal-microbalance [QCM], surface acoustic wave [SAW] devices, tuning forks, cantilevers, flexural plate wave [FPW] devices
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2291/00—Indexing codes associated with group G01N29/00
    • G01N2291/02—Indexing codes associated with the analysed material
    • G01N2291/021—Gases
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2291/00—Indexing codes associated with group G01N29/00
    • G01N2291/04—Wave modes and trajectories
    • G01N2291/042—Wave modes
    • G01N2291/0427—Flexural waves, plate waves, e.g. Lamb waves, tuning fork, cantilever
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02A—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
    • Y02A50/00—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE in human health protection, e.g. against extreme weather
    • Y02A50/20—Air quality improvement or preservation, e.g. vehicle emission control or emission reduction by using catalytic converters
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
    • Y10T29/00—Metal working
    • Y10T29/49—Method of mechanical manufacture
    • Y10T29/49826—Assembling or joining
    • Y10T29/49885—Assembling or joining with coating before or during assembling
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
    • Y10T436/00—Chemistry: analytical and immunological testing
    • Y10T436/17—Nitrogen containing
    • Y10T436/177692—Oxides of nitrogen
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
    • Y10T436/00—Chemistry: analytical and immunological testing
    • Y10T436/17—Nitrogen containing
    • Y10T436/177692—Oxides of nitrogen
    • Y10T436/178459—Only nitrogen dioxide
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
    • Y10T436/00—Chemistry: analytical and immunological testing
    • Y10T436/17—Nitrogen containing
    • Y10T436/177692—Oxides of nitrogen
    • Y10T436/179228—Both nitrogen oxide and dioxide

Definitions

  • GHG green house gases
  • NAQS National Ambient Air Quality
  • the inventors recognize the need for providing gas sensing devices with reduced drift, improved accuracy and high sensitivity. Additionally, the inventors recognize the need for providing gas sensing devices which can accurately detect NO 2 emissions in ranges smaller than parts per million (ppm) in the ambient.
  • the novel sensors described herein provide improved accuracy together with the ability to detect ultra small gas concentrations on the order of parts per billion (ppb), parts per trillion (ppt) or smaller.
  • the devices may be used in micro-scale electromechanical systems.
  • a nitrogen dioxide sensor comprising a first beam having a first functionalized sensing surface capable of sensing nitrogen dioxide, the first beam capable of producing a first resonant frequency; and a second beam having a second functionalized reference surface not capable of sensing nitrogen dioxide, the second beam capable of producing a second resonant frequency, wherein differential sensing of nitrogen dioxide may be performed is provided.
  • the second functionalized reference surface is further altered with respect to a first beam with by adding a polyethylene coating to prevent detection of NO2.
  • the sensor has low drift with respect to prior art differential resonant sensors, which are using bare surface on the second beam.
  • the sensor has low drift; as compared to conventional differential resonant sensors, which use bare surfaces on the second beam.
  • a "low drift" sensor refers to a sensor with a baseline drift which is at least five times lower than the sensor resolution itself, thus allowing the sensor to preserve its accuracy within its entire dynamic range, for its entire sensor lifetime.
  • the senor is a nanosensor capable of performing differential sensing by monitoring changes in the resonant frequency of the first beam relative to the resonant frequency of the second beam.
  • the first and second beams of the sensor may be located on a single silicon substrate or on different silicon substrates.
  • the first and second beams may be functionalized in any suitable manner, such as with one or more soft bases (e.g., a conjugated aromatic hydrocarbon, a carbon nanotube, and a ferrocene moiety), each having comparable visco-elastic properties.
  • each beam is functionalized with a different soft base.
  • the first beam of the sensor may have a functionalized surface containing ferrocene moieties as sensitive groups for nitrogen dioxide detection, while the second beam may have a functionalized surface further containing a coating of polyethylene to prevent detection of nitrogen dioxide.
  • the senor further comprises a first frequency measuring circuit for measuring the resonant frequency of the first beam; a second frequency measuring circuit for measuring the resonant frequency of the second beam: and a control for analyzing the signals from the first frequency measuring circuit and the second frequency measuring circuit, wherein a differential frequency equivalent to the first frequency minus the second frequency is determinable, wherein differential sensing of nitrogen dioxide exposure is performed.
  • Embodiments of the invention further comprise a method comprising functionalizing a silicon surface to detect NO 2 ; and altering a portion of the functionalized silicon surface to prevent detection of NO 2 .
  • the silicon surface is functionalized with carbon nanotube moieties by first preparing an amino-terminated silicon surface or an iodine-terminated silicon surface.
  • the silicon surface is functionalized through reaction of carboxylic carbon nanotubes with an alcohol-terminated silicon surface in the presence of dicyclohexil carbodiimide in DMSO.
  • the silicon surface is functionalized through reaction of a compound synthesized by reacting carbon nanotubes with allyl iodide and potassium and hydrogen terminated silicon surfaces.
  • a portion of the functionalized silicon surface has been altered to prevent detection of nitrogen dioxide is altered by direct printing of a polyethylene coating.
  • the invention further comprises connecting frequency measuring circuits to a suspended vibrating beam (e.g., clamped-clamped silicon beam, cantilever, silicon nanowire as a portion of a silicon chip) containing the functionalized silicon surface in order to produce differential resonance frequency changes; connecting inputs of a mixer to the output of the frequency measuring circuits to measure the differential resonance frequency changes; and outputting the differential resonance frequency changes to a presentation device.
  • a suspended vibrating beam e.g., clamped-clamped silicon beam, cantilever, silicon nanowire as a portion of a silicon chip
  • Embodiments of the invention further comprise a method of detecting nitrogen dioxide comprising exposing first and second beams to nitrogen dioxide, wherein the first beam has a functionalized surface to detect nitrogen dioxide and the second beam has a functionalized surface altered to prevent detection of nitrogen dioxide; and comparing the resonance frequency of the first beam to the resonance frequency of second beam, wherein an amount of nitrogen dioxide exposure is determined.
  • the first and second beams are nano-beams and the second beam is altered with a polyethylene coating.
  • Embodiments of the novel NO 2 gas sensors described herein are low in cost and high in performance with low drift detection capabilities-and excellent mass resolution.
  • resonant differential principles are applied to silicon nano-electromechanical systems (NEMS), thus allowing for detection in the range of hundreds of zeptograms of NO 2 , with baseline drift elimination.
  • NEMS silicon nano-electromechanical systems
  • FIG. 1 is a simplified illustration of a nitrogen dioxide (NO 2 ) resonator according to an example embodiment.
  • FIG. 2 is an enlarged view illustrating a portion of the NO 2 sensor shown in FIG. 1 according to an example embodiment.
  • FIG. 3 is a simplified illustration of a direct printing system for preparing a functionalized surface according to an example embodiment.
  • Conventional differential bio-chemical sensing devices based on the resonance principle may include a resonant sensing loop, a resonant reference loop and an electronic mixer which outputs the difference between the resonance frequencies provided by each of the sensing and reference loops. Both loops comprise an identical electronic readout circuit for frequency measurement and a device to determine the resonance frequency.
  • the resonant sensing loop comprises a device exposed to the external environment to be monitored, i.e. a bio-chemical resonant sensor having a functionalized surface or a sensing layer chemically designed to adsorb or absorb and detect the desired bio-chemical component (gas or bio component), by its reversible reaction with the functionalized surface.
  • the resonant reference loop in these prior art differential bio-chemical resonant sensors comprises a "vibrating" device with the same geometry as the sensor, but having a bare surface or an uncoated surface.
  • the prior art bare (uncoated) surface is likely to have a different response to external conditions (e.g., humidity in the ambient air, temperature, ageing, and the like) as compared to the sensing layer.
  • external conditions e.g., humidity in the ambient air, temperature, ageing, and the like
  • the "common mode signals” such as humidity, ageing of the sensing layer, and the like, cannot be eliminated at the mixer level, as they are not present in both terms to be subtracted.
  • Such influences i.e., susceptibility to external effects, result in a significant amount of "baseline drift,” leading to reduced accuracy.
  • the prior art sensors are only able to discern gaseous levels in the parts per million (ppm) range.
  • embodiments of the present invention comprise a bio-chemical differential sensor with a resonant reference loop comprising a functionalized reference layer on the reference beam surface with visco-elastic properties similar to the functionalized sensing layer, but altered (such as with a coating) to provide a functionalized reference beam having no sensing properties.
  • a non-sensing functionalized reference surface in the reference loop allows, for the first time, full scale differential sensing which is not only highly accurate and drift- free, but capable of discerning NO 2 content in extremely small amounts of NO 2 , such as in the zeptogram range.
  • FIG. 1 illustrates an example of nitrogen dioxide sensor 10.
  • the nitrogen dioxide sensor 10 includes a substrate 11 with a first beam 12 and a second beam 16 formed on the substrate 11. Although the first and second beams 12, 16 are shown on the same substrate 11, embodiments are contemplated where the first and second beams 12, 16 could be also on different substrates.
  • FIG. 2 is an enlarged view illustrating a portion of the nitrogen dioxide sensor shown in FIG. 1 .
  • the first beam 12 includes a first functionalized sensing surface (i.e., first sensing monolayer 14 and the second beam 16 includes a second functionalized reference layer 18 (i.e., a coating layer deposited on top of the same functionalized monolayer applied on both first and second beam).
  • first functionalized sensing surface i.e., first sensing monolayer 14
  • the second beam 16 includes a second functionalized reference layer 18 (i.e., a coating layer deposited on top of the same functionalized monolayer applied on both first and second beam).
  • Each of the functionalized sensing and reference surfaces 14 and 18, respectively possess similar visco-elastic properties and ageing properties and will respond similarly to ambient temperature and humidity (e.g., similar hydrophilic or hydrophobic properties).
  • a “functionalized surface” refers herein to a beam surface modified in a manner to perform a desired function, i.e., to either sense (and thus to obtain a sensing beam) or to not sense (and thus obtain a reference beam) by means of monolayers grown or applied on the beam.
  • a desired function i.e., to either sense (and thus to obtain a sensing beam) or to not sense (and thus obtain a reference beam) by means of monolayers grown or applied on the beam.
  • the first and second sensing and reference functionalized surfaces, 14 and 18, respectively are each functionalized in a different manner according to any suitable method, such as any one of Schemes 1-5 described herein.
  • the functionalized surfaces 14, 18 may be part of the first and second beams 12, 16, respectively or formed as part of a layer or coating further added to the initially modified surface of the second beam 16, to obtain a first functionalized sensing beam 12 and a functionalized non-sensing reference beam 16.
  • a functionalized surface may be altered by some method to inhibit sensing or detection of nitrogen dioxide on the second beam 16.
  • the second functionalized reference surface 18, however, has further been altered through deposition of a coating or barrier layer to prevent the second functionalized reference surface 18 from sensing NO 2 , thus allowing the second functionalized reference surface 18 to function as a non-sensing functionalized reference surface.
  • the nitrogen dioxide sensor 10 performs differential sensing of nitrogen dioxide by monitoring changes in the resonant frequency of the first beam 12 relative to the resonant frequency of the second beam 16. Therefore, the nitrogen dioxide sensor 10 may further include a first frequency measuring device 20 for measuring the resonant frequency of the first beam 12 and a second frequency measuring device 19 for measuring the resonant frequency of the second beam 16.
  • the frequency measuring circuits 19 and 20 may operate, for example, according to the principle of phase lock loop circuits. (See, for example, US Patent No. 6, 722,200 , (hereinafter '200), which is hereby incorporated by reference in its entirety).
  • Each of the circuits 19 and 20 provide the resonance frequency of the corresponding beams.
  • the invention provides an all differential resonant sensor, where the resonance frequencies of the two beams are subtracted at the level of an electronic reader, in order to get a frequency difference which will eliminate the common mode signal due to humidity, ageing, etc, as is discussed in U.S. Patent Application Serial No. 12/617,893 entitled, "All-Differential Resonant Nanosensor Apparatus and Method, filed on November 13, 2009 (hereinafter "'893), which is hereby incorporated by reference herein in its entirety.
  • a differential reading electronic circuit comprising a mixer with the two frequency signals at the input and with the frequency difference at the output may be interconnected with each resonant beam pair (sensing and reference) for signal processing. By subtracting the frequency response from the sensing loop and the reference loop, a drift-free frequency signal for NO 2 may be obtained.
  • two electronic oscillators may be used for the reading of the two resonance frequencies. In this case, each oscillator is made of an amplifier having in its feedback loop a vibrating beam.
  • the first and second frequency measuring circuits 19, 20 may be a variety of electronic circuits. In one embodiment, the first and second frequency measuring circuits 19, 20 are similar to the circuits disclosed in U.S. Patent No. 6,722,200 , which is hereby incorporated by reference in its entirety. In some embodiments, the first and the second frequency measuring circuits 19, 20 send signals to a mixer or control 22 for differential sensing as described in '893, supra. Specifically, as mentioned above, at the output of the mixer 22, the difference of the frequencies measured by the two frequency measuring circuits 19 and 20. The frequency difference will give a drift free, high accuracy information about the gas to be detected
  • FIG. 3 is an illustration of one embodiment of a single head direct printing system 30 useful herein.
  • deposition material (DM) 35 uses a distribution system for local, selective and additive direct deposition of the desired material.
  • the print head 32 may be supplied with atomized DM from a an atomizer module (AM) 33 connected to a DM source 35 and a suitable gas supply, as is known in the art, for deposition of the atomized DM 33 on a silicon surface (e.g., wafer) 37 to form a functionalized reference layer 39 (such as an ultra thin reference layer) on the silicon wafer 37 as shown in FIG. 3 .
  • the silicon surface 37 may comprise any configuration and size of silicon substrate. In the embodiment shown in FIGS. 1 and 2 , for example, such a deposit would be present only on each second beam 16 of a chip.
  • the DM 35 necessarily comprises a material chemically designed to essentially "de-functionalize" the second functionalized sensing surface 42, to produce a non-sensing functionalized reference surface.
  • DM 35 may be polyethylene.
  • Such a coating alters the functionalized sensing surface. The coating is dispensed selectively and without use of a mask on the existing functionalized sensing layer already present. Referring again to FIGS. 1 and 2 , this functionalized layer is located on the reference beam 16.
  • Direct printing may be considered a type of post-processing performed on a silicon substrate, such as a wafer, prior to subsequent steps, such as packaging and dicing.
  • a silicon substrate such as a wafer
  • subsequent steps such as packaging and dicing.
  • a differential NO 2 resonant nano-sensor containing a tandem of a sensing monolayer obtained on the surface of a Si vibrating beam and a reference (non-sensing) monolayer obtained on the surface of a Si reference vibrating beam, both vibrating beams being located on the same chip and being excited to resonance and interrogated with identical electronics is provided.
  • a barrier layer or coating such as a polyethylene coating on the reference beam, a non-sensing reference beam is obtained.
  • the polyethylene coating is applied by direct selectively printing of liquid polyethylene, which may be further thermally treated to get a solid state ultra thin coating (i.e., such as between about three (3) up to no more than about five (5) nanometers (nm) in thickness, although portions of the coating may exceed five (5) nm), thereby creating the non-sensing functionalized reference beam.
  • a solid state ultra thin coating i.e., such as between about three (3) up to no more than about five (5) nanometers (nm) in thickness, although portions of the coating may exceed five (5) nm
  • functionalization of all the Si surfaces is provided with a NO 2 sensing monolayer containing CNT terminal groups produced through chemical synthesis of the CNTs with a suitable amino alcohol, such as 4 amino-1 butanol, 5 amino 1-pentanol or 6 amino 1-hexanol.
  • a suitable unsaturated alcohol such as 3-iodo, 1-propene, 4 iodo-1 butene, 5 iodo-1 pentene.
  • functionalization of all the Si surfaces is provided with a NO 2 sensing monolayer containing CNT terminal group connected directly to silicon surface by CH 2 groups.
  • functionalization of all the Si surfaces is provided with a NO 2 sensing monolayer containing ferrocene moieties.
  • the chemical design of the functional sensing group in the sensing monolayer is based on Pearson's Hard Soft (Lewis) Acid Base (HSAB) principle.
  • HSAB Hard Soft Acid Base
  • a hard Lewis base prefers to bond to a hard Lewis acid
  • a soft Lewis base prefers to bond to a soft Lewis acid.
  • NO 2 is a soft acid, it should have a preference for a soft base.
  • Soft bases useful herein include, but are not limited to, mercaptans, thioethers, benzene and other conjugated aromatic hydrocarbons.
  • Other soft bases include carbon nanotubes (CNTs) and ferrocene moieties. Such molecules are considered soft bases due to their aromatic character and the reversible nature of their interactions with other charged particles.
  • both types of molecules can be described in terms of Kekule structures.
  • double-wall CNT's are used, due to their reduced noise, resulting in higher mass resolution and sensitivity, although the invention is not so limited.
  • single-wall or multi-wall CNTs are used.
  • the soft bases are essentially being used as anchors for NO 2 sensing.
  • the two beams are functionalized identically in a first stage, which may help in conferring similar ageing properties.
  • a monolayer of a compound capable of "poisoning" the sensing surface is deposited to eliminate the ability of the reference surface to function as a sensing surface, i.e., to prevent sensing from occurring on the reference beam.
  • polyethylene is applied on top of the previously functionalized surface to produce the reference layer.
  • the processed substrates may be subject to treatments (such as diluted HF) in a gaseous phase rather than a liquid phase, in order to minimize the risk of suspended beam sticking to the substrate.
  • treatments such as diluted HF
  • a silicon substrate is functionalized with a CNT moiety according to the following steps:
  • Si substrates with exposed Si surfaces covered with native SiO 2 are rinsed with deionized water to produce one or more rinsed Si substrates.
  • the one or more rinsed Si substrates are immersed in a solution of hydrogen fluoride (HF) for a period sufficient to remove native SiO 2 and generate a Si-H surface, thus producing one or more Si-H substrates.
  • HF hydrogen fluoride
  • the one or more Si-H substrates are immersed in a 2% HF solution for approximately one (1) minute:
  • the one or more H-terminated Si substrates are exposed to a stream of ozone for a time sufficient to produce one or more oxidized Si substrates, each having a hydroxyl terminated surface thereon.
  • the one or more H-terminated Si substrates are exposed for at least about five (5) minutes (min) up to about 60 min, such as about 10 to about 40 min, about 20 to about 30 min, or any range there between, such as about 24 to 26 min.
  • the one or more oxidized Si substrates are placed in a flask containing an amino alcohol (e.g., 3 aminol-propanol) and heated in an inert atmosphere (e.g., nitrogen) for a time and at a temperature sufficient to produce one or more Si substrates, each having an amino (NH 2 ) terminated silicon surface.
  • an amino alcohol e.g., 3 aminol-propanol
  • an inert atmosphere e.g., nitrogen
  • the one or more oxidized Si substrates are heated at a temperature of at least about 100 °C, such as at least about 140 up to about 160 °C, such as about 148 to about 152 °C, or any range there between, for at least about two (2) (hr) up to six (6) hrs, such as about 3.5 to about 4.5 hrs, or any range there between, further including about four (4) hrs.
  • the one or more Si substrates are rinsed with an unsaturated alcohol, such as isopropyl alcohol, deionized water and dried under a nitrogen stream to produce one or more processed Si substrates, with each of the one or more processed Si substrates having a rinsed and dried NH 2 terminated silicon surface:
  • one or more CNTs are sonicated in a mixture of nitric acid and sulfuric acid at a suitable ratio (e.g.,1:3) at a frequency, power and duration sufficient to functionalize the one or more CNTs with a carboxylic group to produce one or more carboxylic CNTs:
  • the one or more carboxylic CNTs are mixed with tionyl chloride (SOCl 2 ) in an amount sufficient to convert the carboxylic acid moieties to carboxylic chloride moieties to produce one or more COCl-CNTs:
  • the one or more CNT-COCls (b) are reacted with the one or more Si substrates (a) having rinsed and dried NH 2 terminated silicon surfaces (from Step #5) to produce one or more Si substrates coated or functionalized with one or more CNT moieties for NO 2 detection: No further processing is performed on the substrates to be used as sensing beams.
  • a silicon substrate is functionalized with a CNT moiety by an alternate method.
  • the process proceeds as outlined in Steps 1 and 2 above. Thereafter:
  • the one or more H-terminated Si substrates are heated at a temperature of at least about 100 °C, such as at least about 140 up to about 160 °C, such as about 148 to about 152 °C, or any range there between, for at least about two (2) (hr) up to six (6) hrs, such as about 3.5 to about 4.5 hrs, or any range there between, further including about four (4) hrs.
  • the one or more iodine terminated (functionalized) Si substrates are cooled in ambient conditions down to room temperature.
  • one or more CNTs are sonicated in a mixture of nitric acid and sulfuric acid at a suitable ratio (e.g.,1:3) at a frequency, power and duration sufficient to functionalize the one or more CNTs with a carboxylic group to produce one or more carboxylic CNTs:
  • the one or more carboxylic CNTs are sonicated in a suitable amount of sodium hydroxide (NaOH) at a frequency, power and duration sufficient to form one or more sodium salt CNTs:
  • the one or more sodium salt CNT's (b) are reacted with the one or more Si substrates (a), each having rinsed and dried iodine-terminated silicon surfaces (from Step #5) in the presence of a sufficient amount of a phase transfer catalyst (e.g., tetramethylammonium iodide) at a temperature in the range of 40-60 °C sufficient to produce one or more Si substrates coated or functionalized with one or more CNT moieties for NO 2 detection:
  • a phase transfer catalyst e.g., tetramethylammonium iodide
  • a silicon substrate is functionalized with a CNT moiety by an alternate method.
  • the process proceeds as outlined in Steps 1 and 2 above. Thereafter:
  • the one or more H-terminated Si substrates are heated to a temperature of 100 °C, such as at least about 140 up to about 160 °C, such as about 148 to about 152 °C, or any range there between, for at least about two (2) (hr) up to six (6) hrs, such as about 3.5 to about 4.5 hrs, or any range there between, further including about four (4) hrs.
  • the one or more functionalized Si substrates are cooled under ambient conditions down to room temperature.
  • the one or more cooled functionalized Si substrates are rinsed with an alcohol, such as ethanol and deionized water dried under nitrogen stream to produce one or more processed Si substrates:
  • one or more CNTs are sonicated in a mixture of nitric acid and sulfuric acid at a suitable
  • the one or more carboxylic CNTs (b) are reacted with the one or more Si substrates (a) having rinsed and dried functionalized silicon surfaces (from Step #6) in the presence of a dicyclohexil carbodiimide (DCC) in DMSO, at a temperature, such as 40-60°C, sufficient to produce one or more Si substrates coated or functionalized with one or more CNT moieties for NO 2 detection. No further processing is performed on the substrates to be used as sensing beams:
  • DCC dicyclohexil carbodiimide
  • a silicon substrate is functionalized with a CNT moiety by yet another alternate method.
  • the process proceeds as outlined in Steps 1 and 2 above. Thereafter:
  • the one or more H-terminated Si substrates synthesized in step 3 are heated in a non-polar solvent, such as toluene under conditions sufficient to produce one or more functionalized silicon substrates.
  • a non-polar solvent such as toluene
  • the mixture is heated to a temperature of a100 °C, such as at least about 140 up to about 160 °C, such as about 148 to about 152 °C, or any range there between, for at least about two (2) (hr) up to six (6) hrs, such as about 3.5 to about 4.5 hrs, or any range there between, further including about four (4) hrs.
  • the one or more functionalized Si substrates are cooled in ambient conditions down to room temperature.
  • a silicon substrate is functionalized with a ferrocene moiety.
  • the process proceeds as outlined in Steps 1 and 2 above. for getting a hydrogen terminated silicon surface Thereafter:
  • the one or more H-terminated Si substrates synthesized in step 2 are combined with vinyl ferrocene together with a non-polar solvent, such as toluene, under conditions sufficient to produce one or more functionalized silicon substrates.
  • a non-polar solvent such as toluene
  • the mixture is heated to a temperature of a100 °C, such as at least about 140 up to about 160 °C, such as about 148 to about 152 °C, or any range there between, for at least about two (2) (hr) up to six (6) hrs, such as about 3.5 to about 4.5 hrs, or any range there between, further including about four (4) hrs.
  • the one or more functionalized Si substrates are cooled in ambient conditions down to room temperature.
  • the one or more functionalized Si substrates are rinsed with an alcohol, such as ethanol and deionized water and dried under nitrogen stream to produce one or more dried and processed Si substrates.
  • an alcohol such as ethanol and deionized water
  • a novel a low cost, high performance NO 2 gas sensor is provided which uses resonant differential principles.
  • this technology is applied to silicon nano-electromechanical systems (NEMS).
  • NEMS silicon nano-electromechanical systems

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  • Combustion & Propulsion (AREA)
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  • Medicinal Chemistry (AREA)
  • Investigating Or Analyzing Materials By The Use Of Fluid Adsorption Or Reactions (AREA)
EP09178792A 2009-12-11 2009-12-11 Differentialresonatoren zur NO2-Detektion und damit verbundene Verfahren Withdrawn EP2333531A1 (de)

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US12/962,067 US8563319B2 (en) 2009-12-11 2010-12-07 Differential resonators for NO2 detection and methods related thereto

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